1. Field of the invention
The present invention relates to a radiation image detecting device for use in a radiation imaging system and a method for detecting start of irradiation with radiation.
2. Description Related to the Prior Art
In the medical field, a radiation imaging system using radiation, for example, X-rays, for image diagnosing has been known. The X-ray imaging system is composed of an X-ray source, an X-ray source controller, and an X-ray image detecting device. The X-ray source generates X-rays. The X-ray source controller controls the X-ray source. The X-ray image detecting device detects an X-ray image formed by the X-rays passed through a subject. An FPD (flat panel detector) is used as an X-ray image detecting device. The FPD includes a TFT (thin film transistor) active matrix substrate with a plurality of pixels arranged thereon. Each pixel accumulates signal charge corresponding to an amount of X-rays incident on the pixel. Thereby, the FPD detects an X-ray image representing image information of the subject, and outputs the X-ray image as digital image data.
The X-ray image detecting device using the FPD, unlike that using a film or an IP (imaging plate), needs to be synchronized with the X-ray source such that the FPD accumulates signal charge (hereinafter referred to as the accumulation operation) concurrently with the X-ray emission from the X-ray source. Accordingly, a controller, for example, a console of the X-ray image detecting device synchronizes the start of the accumulation operation by the FPD with the start of the X-ray emission by the X-ray source. The X-ray emission by the X-ray source is triggered by an emission start switch connected to the X-ray source controller. Namely, the controller receives an emission start signal from the emission start switch, and outputs this signal as a synchronization signal to the X-ray image detecting device. Upon receiving the synchronization signal, the X-ray image detecting device starts the accumulation operation to capture an X-ray image.
However, when the X-ray image detecting device and the X-ray source controller are manufactured by different makers, a synchronization control interface of the X-ray image detecting device or its controller may be incompatible with that of the X-ray source in the specifications of a cable and a connector, the format of the synchronization signal, and the like. To avoid this, various self-detection techniques for the X-ray image detecting device are proposed to detect the start of X-ray irradiation without using the synchronization signal so as to synchronize with the X-ray source (see U.S. Patent Application Publication No. 2003/0086523 corresponding to Japanese Patent Laid-Open Publication No. 2003-126072, U.S. Pat. No. 6,797,960 corresponding to Japanese translation No. 2002-543684 of PCT International Publication, U.S. Patent Application Publication No. 2010/0054405 A1, now U.S. Pat. No. 8,045,680 B2, corresponding to Japanese Patent Laid-Open Publication No. 2008-125903).
According to the self-detection techniques disclosed in the above patent documents, the X-ray image detecting device may erroneously detect the start of the X-ray irradiation when noise (hereinafter referred to as the impact noise) caused by impact, vibration, or the like occurs, which triggers a detection process of an X-ray image. However, the above patent documents do not describe or even suggest the problem of the false detection due to the impact noise and measures against it.